import pygame;
class Ship():
	def __init__(self,ai_settings,screen):
		"""初始化飞船并设置其初始位置"""
		self.screen = screen;
		self.ai_settings = ai_settings;
		
		#加载飞船图像并获取其外接矩形
		self.image = pygame.image.load('images/ship.bmp');
		self.rect = self.image.get_rect();
		self.screen_rect = screen.get_rect();
		
		#将每艘新飞船放在屏幕底部中央
		self.rect.centerx = self.screen_rect.centerx;
		self.rect.bottom = self.screen_rect.bottom;
		
		#在飞船的属性center中存储小数值
		self.center = float(self.rect.centerx);
		
		#移动标志
		self.moving_right = False;
		self.moving_left = False;
		
	def blitme(self):
		'''在指定位置绘制飞船'''
		self.screen.blit(self.image,self.rect);
	
	def update(self):
		'''根据移动标志来调整飞船的位置'''
		#更新飞船的center值，而不是rect
		if self.moving_right and self.rect.right < self.screen_rect.right:
			self.center += self.ai_settings.ship_speed_factor;
		if self.moving_left and self.rect.left > 0:
			self.center -= self.ai_settings.ship_speed_factor;
			
		#根据self.center 更新rect对象
		self.rect.centerx = self.center;
			